#39 Stopping MantaRay

[Amir Shevat]

All MantaRay objects should be cleared from memory and
all MantaRay threads should stop when there is no
longer need for them in these cases:

1) All connections have been closed and these
connections had only subscribers/consumers.

2) All connections have been closed and these
connections had producers/publishers and all messages
produced/published have been delivered

--Amir